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Node.JS and Express res.redirect() not enabling new webpage

I'm trying to save a variable to a text file, but if the variable isn't found when using spotifyApi.clientCredentialsGrant(), then I want my server to redirect to app.get('/error', function(req, res) {}); which displays a different webpage, but it's returning the error:
(node:11484) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
How can I get around this error to display the webpage error.html?
I don't have access to EJS or window.location because it conflicts with other files and it's a node.js program, respectively.
app.get('/', function (req, res) {
res.sendFile(path.join(__dirname, '/public', 'homepage.html'));
try {
spotifyApi.clientCredentialsGrant()
.then(function (data) {
// Save the access token so that it's used in future calls
client_cred_access_token = data.body['access_token'];
console.log(client_cred_access_token);
console.log('Client Credentials Success!');
}, function (err) {
console.log('Something went wrong when retrieving an access token', err.message);
throw err;
});
fs.writeFile("./public/client_cred_token.txt", '', function (err) {
console.log('Clearing previous access token');
});
fs.writeFile("./public/client_cred_token.txt", client_cred_access_token, function (err) {
if (err) return console.log(err);
});
fs.readFile('./public/client_cred_token.txt', function (err, data) {
if (err) throw err;
console.log("Saved Client Credentials as: %s", data)
});
}
catch (err) {
res.redirect('/error');
}
});
Key takeaway from the accepted answer is to not send any HTML/files to the server until it's confirmed which one is needed.

You are calling res.sendFile() first and then if you later get an error, you are also calling res.redirect('/error') which means you'll be trying to send two responses to one http request which triggers the error you see. You can't do that.
The solution is to call res.sendFile() at the end of all your other operations so you can then call it when successful and call res.redirect() when there's an error and thus only call one or the other.
In a difference from the other answer here, I've shown you how to code this properly using asynchronous file I/O so the design could be used in a real server designed to serve the needs of more than one user.
const fsp = require('fs').promises;
app.get('/', async function (req, res) {
try {
let data = await spotifyApi.clientCredentialsGrant();
// Save the access token so that it's used in future calls
client_cred_access_token = data.body['access_token'];
console.log(client_cred_access_token);
console.log('Client Credentials Success!');
await fsp.writeFile("./public/client_cred_token.txt", client_cred_access_token);
let writtenData = await fsp.readFile('./public/client_cred_token.txt');
console.log("Saved Client Credentials as: %s", writtenData);
res.sendFile(path.join(__dirname, '/public', 'homepage.html'));
} catch (err) {
console.log(err);
res.redirect('/error');
}
});

app.get('/', function (req, res) {
try {
spotifyApi.clientCredentialsGrant().then(function (data) {
// Save the access token so that it's used in future calls
let client_cred_access_token = data.body['access_token'];
console.log(client_cred_access_token);
console.log('Client Credentials Success!');
// truncate token file
fs.truncateSync("./public/client_cred_token.txt");
// write token to file
fs.writeFileSync("./public/client_cred_token.txt", client_cred_access_token);
// read token from file again
// NOTE: you could use `client_cred_access_token` here
let data = fs.readFileSync('./public/client_cred_token.txt');
console.log("Saved Client Credentials as: %s", data)
// send homepage to client when no error is thrown
res.sendFile(path.join(__dirname, '/public', 'homepage.html'));
}, function (err) {
console.log('Something went wrong when retrieving an access token', err.message);
throw err;
});
} catch (err) {
res.redirect('/error');
}
});
I swapped all asynchron file opreations with the syncron one.
They throw an error and you dont have to deal with callback chain/flow.
Also i moved the sendFile(...) at the botom in the try block, so when a error is thrown from any syncrhonus function call the sendFile is not reached, and your redirect can be sent to the client.
Otherwise you would send the homepage.html to the client, with all headers, and a redirect is not possible.

Sending file through HTTP request

I tried to receive the file and store it in the multer storage
Node js code
enter code here
app.post('/createLicence', upload.single('photo'),function(req, res ,next) {
// any logic goes here
console.log("filename" ,req.body.name)
if (!req.file) {
console.log("No file received");
return res.send({
success: false
});
} else {
console.log('file received');
var function_name = 'createLicence'
var arguments_array = [req.file.path,'Raghav','Mumbai','Approved']
invoke = require('/Users/sanjeev.natarajan/fabric-samples/fabcar/invoke.js');
invoke.invokechaincode(function_name,arguments_array)
return res.send({
success: true
})
}
});
but i am receiving no file is receivedi have send the request through postman

-
From : https://www.npmjs.com/package/multer
In order to use the multer package, you have first to define a few parameters so that it can work on your fileDirectory.
In your server.js :
let multer = require('multer');
let storage = multer.diskStorage({
destination: function(req, file, cb) {
cb(null, '/path/to/storage/')
},
filename: function(req, file, callback) {
callback(null, file.originalname + '-' + Date.now());
}
});
let upload = multer({
storage: storage
});
Now, configure your route
router.route('/your/payload')
.post(authController.isAuthenticated, upload.any(), albumController.postFile)
Note that upload.any() will allow you to upload multiple different formatted files at once. Feel free to use any other kind of upload.method() depending on your needs.
From this point, multer already is doing its job, however you might want to keep track of the files uploaded on your server.
So, in your own module, the logic is pretty much straight forward :
(I'm assuming that you're using mongoose models since you're not giving much information, but that's not the relevant part anyway)
exports.postFile = async (req, res) => {
if (!req || !req.files || !req.files[0]) return res.status(400).send("Bad request.");
for (let i = 0; req.files[i]; i++) {
await File.create({
path: req.files[i],
originalName: req.files[i].originalName,
mimetype: req.files[i].mimetype,
owner: req.user.userId
}, (err, file) => {
if (err) console.log("Something went wrong: " + err); else {
// Do something with file
}
});
}
return res.status(418).send("I'm a teapot.");
}
This configuration and middleware use is ONLY for testing purpose, never ever let anyone upload something to your server without carefully handle that uploading process (file integrity, resource management, ...). An open uploading system can become a very wide backdoor getting straight to your server.
Hope this helps,
regards.

How to configure API endpoint to receive file from ember-uploader component

I'm trying to figure out how to use ember-uploader, I have the following component (like the one in the README)
export default EmberUploader.FileField.extend({
filesDidChange: function(files) {
const uploader = EmberUploader.Uploader.create({
url: (ENV.APP.API_HOST || '') + '/api/v1/images/',
});
console.log(uploader);
if (!Ember.isEmpty(files)) {
var photo = files[0];
console.log(photo);
uploader.upload(photo)
.then(data => {
// Handle success
console.log("Success uploading file");
console.log(data);
}, error => {
// Handle failure
console.log("ERROR uploading file");
console.log(error);
});
}
}
});
The express API endpoint is listening for a POST request.
var saveImage = (req, res, next) => {
let body = req.body;
res.json({
data: body
});
};
But the body is empty after the request is done. I really don't know how to implement the API endpoint in order to get the file, I tried to see the req object and it doesn't contains the file.
Debugging it, After select a file using the component I get the following info in the console.
Seems that the API endpoint works because I get the following output:
POST /api/v1/images/ 200 27.284 ms - 11
But I can't get the file.

SOLUTION
In Express 4, req.files is no longer available on the req object by
default. To access uploaded files on the req.files object, use a
multipart-handling middleware like busboy, multer, formidable,
multiparty, connect-multiparty, or pez.
Following this blog, the code below was added to the API and the ember-uploader code posted in the question worked as expected.
import formidable from 'formidable';
var saveImage = (req, res, next) => {
var form = new formidable.IncomingForm();
form.parse(req);
form.on('fileBegin', function (name, file){
file.path = __dirname + '/tmp/' + file.name;
});
form.on('file', function (name, file){
res.json({
data: file.name
});
});
};

MYSQL + Node.JS Post Request Confusion

I am very new to networking and I have this code which, when I use a REST API like Postman, does exactly what I want it to do:
router.post('/', function(req,res,next){
var reqObj = req.body;
console.log(reqObj);
req.getConnection(function(err, conn){
if(err)
{
console.error('SQL Connection error: ', err);
return next(err);
}
else
{
var query = conn.query("INSERT INTO coordinates (id,lat,lon) VALUES(3,2,1);");
if(err)
{
console.error('SQL error: ', err);
return next(err);
}
res.json("Coordinates sent.");
}
})
} );
That is, it sends the query request to the MYSQL database. My question is, how do I do this without using Postman to send the POST request?
Thank you.

You can't unless you make a post request from within your application or something. If you don't intend on sending data, you can just make it a GET request by changing
router.post('/', function(req,res,next){
to
router.get('/', function(req,res,next){
Then you can just go to the relevant URL from your browser. If you're using chrome and you just wanna see the JSON data, I'd also recommend installing the JSONView chrome extension.
EDIT
Here's the example request using request-promise
var request = require('request-promise');
var objectData = {
name: 'Bruce',
alias: 'Batman'
};
var options = {
method: 'POST',
uri: 'http://your.api/endpoint/',
body: objectData,
json: true // Automatically stringifies the body to JSON
};
request(options).then(function(response){
// handle success response
}, function(error){
// handle error response
})

How to get parameters of `req` in express node server

I have two paramaters in my UI. One is a file and another is dataObject. In the utils, I have written code as :
importPlan: function (formData, planDTO) {
return axios.post(`${importPlanAPIPath}`, planDTO, formData);
}
In the router, I am sending this as :
router.post('/plans/importPlan/', planController.importPlan);
and in the controller, I have written the request as :
async importPlan(req, res, cb) {
let plan,
planDTO = req.body;
const formData = new FormData(),
file = req.files.file;
formData.append('file', file.data);
console.log('planDTO => ', planDTO);
console.log(file.data, file.name);
try {
plan = await req.clients.planClient.importPlan(formData, planDTO);
} catch (err) {
return cb(err);
}
res.json(plan);
}
In the req.body, I am getting the planDTO but I am not getting any req.files in the req. Also I am using bodyparser to parse the request. I am also using busboybodyparser for multipart/form-data.
Can Somebody please tell what I am doing wrong?
Thanks in advance.

yourparam is parameter name
router.post('/plans/importPlan/:yourparam', planController.importPlan);
async importPlan(req, res, cb) {
var yourparam= req.params.yourparam;
..........
res.json(plan);
}
use this module for file upload https://www.npmjs.com/package/multer